The present invention relates to a dampener roll and more specifically to a dampener roll of the brush type, which is used to transfer dampening fluid from a reservoir to a printing plate in a lithographic printing press.
During operation of a lithographic printing press, dampening fluid is transferred from a reservoir to a printing plate. Brush type dampener rolls have been used to control the amount of dampening fluid transmitted from the reservoir to the printing plate. Examples of known dampeners having brush type rolls are disclosed in U.S. Pat. Nos. 2,868,118; 3,411,441; 3,545,379 and 4,143,596.
During use of these known brush type dampener rolls, the amount of dampening fluid transferred from opposite end portions of the brush roll is less, per unit of length, than the amount of dampening fluid transferred from corresponding units of length of the central portion of the brush roll. It is believed that this is because the bristles at the end portions of the brush roll tend to dry out more than the bristles in the central portion of the roll.
Although it is difficult to be certain exactly why the bristles at the opposite end portions of the brush roll dry out to a greater extent than the bristles in the central portion of the brush roll, it is theorized that this may be due to several different reasons including a transfer of heat to the bristles at the opposite end portions of the brush roll from bearings adjacent to opposite end portions of the brush roll. Also, the bristles at the end portions of the dampener fountain roll may not be wetted to the same extent by adjacent bristles as are bristles at the central portion of the dampener roll. This may be due to the bristles at the end of the roll being more exposed than bristles at the central portion of the roll.
It has previously been suggested that an even transfer of dampening fluid from the brush roll could be obtained by having a greater number of bristles per unit of length of the brush roll at opposite ends of the roll than at the central portion of the roll. When a brush roll having such a construction was tried, it was found that the increased density of the bristles at opposite ends portions of the roll was not satisfactory. Thus, even through the number of bristles per unit of length at the end portions of the brush roll was greater than the number of bristles per unit of length at the central portion of the roll, a satisfactory rate of transfer of dampening fluid along the length of the brush roll was not obtained.